Three-dimensional printing

ABSTRACT

Described herein are kits, methods, and systems for printing metal three-dimensional objects. In an example, described is a multi-fluid kit for three-dimensional printing comprising: a first fluid comprising a first liquid vehicle comprising metal or metal precursor particles; and a second fluid comprising a second liquid vehicle comprising latex polymer particles dispersed therein, wherein the latex polymer particles have an average particle size of from about 10 nm to about 300 nm, and wherein the metal or metal precursor particles comprise metal nanoparticles, metal oxide nanoparticles, metal oxide nanoparticles and a reducing agent, or combinations thereof.

BACKGROUND

Three-dimensional (3D) printing may be an additive printing process usedto make three-dimensional solid parts from a digital model. 3D printingcan be often used in rapid product prototyping, mold generation, moldmaster generation, and short run manufacturing. Some 3D printingtechniques are considered additive processes because they involve theapplication of successive layers of material. This is unlike customarymachining processes, which often rely upon the removal of material tocreate the final part. 3D printing can often use curing or fusing of thebuilding material, which for some materials may be accomplished usingheat-assisted extrusion, melting, or sintering.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of examples of the present disclosure will become apparent byreference to the following detailed description and drawings, in whichlike reference numerals correspond to similar, though perhaps notidentical, components. For the sake of brevity, reference numerals orfeatures having a previously described function may or may not bedescribed in connection with other drawings in which they appear.

FIG. 1 is a simplified isometric view of an example 3D printing systemdisclosed herein;

FIGS. 2A through 2F are schematic views depicting the formation of apatterned green part, a cured green part, an at least substantiallypolymer-free gray part, and a 3D metal part using examples of a 3Dprinting method disclosed herein;

FIG. 3 is a flow diagram illustrating another example of a 3D printingmethod disclosed herein;

FIGS. 4(a)-(d) show Scanning Electron Microscope (SEM) photographs of anevolution of latex polymer binder fluid deposited on stainless steelpowder and then pulse heated through different temperatures;

FIGS. 5(a)-(f) show SEM photographs of an evolution of metal oxidebinder fluid and latex polymer binder fluid deposited sequentially onstainless steel powder and then pulse heated through differenttemperatures;

FIGS. 6(a)-(c) show SEM photographs of an evolution of metal oxidebinder fluid and latex polymer binder fluid deposited in different orderand layers on stainless steel powder and then pulse heated throughdifferent temperatures; and

FIG. 7 shows a 2500× magnification of FIG. 6(c).

DETAILED DESCRIPTION

In some examples of three-dimensional (3D) printing, a binder fluid(also known as a liquid functional agent/material) is selectivelyapplied to a layer of build material in a powder bed. The application ofa layer of build material and then applying a binder fluid layer withrepetition of these steps can lead to form a green part (also referredto as a green body) in the powder bed. The binder fluid may include abinder that holds the build material of the green part together. Thegreen part may then be exposed to electromagnetic radiation and/or heatto sinter the build material in the green part to form the 3D part.

Examples of the 3D printing kits, methods, and systems disclosed hereinutilize a single binder fluid or a multi-fluid binder. The single binderfluid or one of the fluids in the multi-fluid binder include polymerparticles, in order to produce a patterned green part from metal powderbuild material, and also utilize heat to activate the polymer particlesand create a cured green part. The cured green part can be removed fromthe metal powder build material that was not patterned with the binderfluid, without deleteriously affecting the structure of the cured greenpart. The extracted, cured green part can then undergo de-binding toproduce an at least substantially polymer-free gray part, and the atleast substantially polymer-free gray part may then undergo sintering toform the final 3D printed part/object.

The single binder fluid can further include metal or metal precursorparticles which can include metal nanoparticles, metal oxidenanoparticles, metal oxide nanoparticles and a reducing agent, orcombinations thereof, in order to produce a patterned green part frommetal powder build material, and also utilize heat to form metallicconnections and create a cured green part. The cured green part can beremoved from the metal powder build material that was not patterned withthe binder fluid, without deleteriously affecting the structure of thecured green part. The extracted, cured green part can then undergode-binding to produce an at least substantially polymer-free gray part,and the at least substantially polymer-free gray part may then undergosintering to form the final 3D printed part/object.

The multi-fluid binder can include a separate binder fluid from thepolymer particle containing fluid. This separate binder fluid caninclude metal or metal precursor particles which can include metalnanoparticles, metal oxide nanoparticles, metal oxide nanoparticles anda reducing agent, or combinations thereof, or combinations thereof, inorder to produce a patterned green part from metal powder buildmaterial, and also utilize heat to form metallic connections and createa cured green part. The cured green part can be removed from the metalpowder build material that was not patterned with the binder fluid,without deleteriously affecting the structure of the cured green part.The extracted, cured green part can then undergo de-binding to producean at least substantially polymer-free gray part, and the at leastsubstantially polymer-free gray part may then undergo sintering to formthe final 3D printed part/object.

As used herein, the term “bound metal object” or “patterned green part”refers to an intermediate part that has a shape representative of thefinal 3D printed part and that includes metal powder build materialpatterned with the binder fluid. In the patterned green part, the metalpowder build material particles may or may not be weakly bound togetherby one or more components of the binder fluid and/or by attractiveforce(s) between the metal powder build material particles and thebinder fluid. In some instances, the mechanical strength of thepatterned green part is such that it cannot be handled or extracted froma build material platform. Moreover, it is to be understood that anymetal powder build material that is not patterned with the binder fluidis not considered to be part of the patterned green part, even if it isadjacent to or surrounds the patterned green part.

As used herein, the term “cured green part” refers to a patterned greenpart that has been exposed to a heating process that initiates meltingof the polymer particles and/or initiates melting of the metal or metalprecursor particles. The heating process may also contribute to theevaporation of the liquid components of the binder fluid(s). Compared tothe patterned green part, the mechanical strength of the cured greenpart is greater, and in some instances, the cured green part can behandled or extracted from the build material platform.

It is to be understood that the term “green” when referring to thepatterned green part or the cured green part does not connote color, butrather indicates that the part is not yet fully processed and/orcompleted.

As used herein, the term “at least substantially polymer-free gray part”refers to a cured green part that has been exposed to a heating processthat initiates thermal decomposition of the polymer particles so thatthe polymer particles are at least partially removed. In some instances,volatile organic components of or produced by the thermally decomposedpolymer particles are completely removed and a very small amount ofnonvolatile residue from the thermally decomposed polymer particles mayremain (e.g., <1 wt % of the initial binder). In other instances, thethermally decomposed polymer particles (including any products andresidues) are completely removed. In other words, the “at leastsubstantially polymer-free gray part” refers to an intermediate partwith a shape representative of the final 3D printed part and thatincludes metal powder build material bound together as a result of i)weak sintering (i.e., low level necking between the particles, which isable to preserve the part shape), or ii) a small amount of the curedpolymer particles remaining, or iii) capillary forces and/or Van derWaals resulting from polymer particle removal, and/or iv) anycombination of i, ii, and/or iii.

It is to be understood that the term “gray” when referring to the atleast substantially polymer-free gray part does not connote color, butrather indicates that the part is not yet fully processed.

The at least substantially polymer-free gray part may have porositysimilar to or greater than the cured green part (due to polymer particleremoval), but the porosity is at least substantially eliminated duringthe transition to the 3D printed part.

As used herein, the terms “three-dimensional object,” “3D object,” “3Dprinted part,” “3D part,” or “metal part” refer to a completed, sinteredpart.

In the examples disclosed herein, the single binder fluid or multi-fluidbinders when applied to a layer of metal powder build material, theliquid vehicle in the fluid(s) is capable of wetting the build materialand the polymer particles and/or the metal or metal precursor particlesare capable of penetrating into the microscopic pores of the layer(i.e., the spaces between the metal powder build material particles).

3D Printing Kits Multi-Fluid Kits

In the examples disclosed herein, a multi-fluid kit forthree-dimensional printing is described. The multi-fluid kit cancomprise a first fluid comprising a first liquid vehicle comprisingmetal or metal precursor particles; and a second fluid comprising asecond liquid vehicle comprising latex polymer particles dispersedtherein, wherein the latex polymer particles have an average particlesize of from about 10 nm to about 300 nm, and wherein the metal or metalprecursor particles comprise metal nanoparticles, metal oxidenanoparticles, metal oxide nanoparticles and a reducing agent, orcombinations thereof.

The latex polymer particles can be made from (A) a co-polymerizablesurfactant chosen from polyoxyethylene alkylphenyl ether ammoniumsulfate, sodium polyoxyethylene alkylether sulfuric ester,polyoxyethylene styrenated phenyl ether ammonium sulfate, or mixturesthereof, and (B) styrene, p-methyl styrene, α-methyl styrene,methacrylic acid, acrylic acid, acrylamide, methacrylamide,2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropylacrylate, 2-hydroxypropyl methacrylate, methyl methacrylate, hexylacrylate, hexyl methacrylate, butyl acrylate, butyl methacrylate, ethylacrylate, ethyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexylmethacrylate, propyl acrylate, propyl methacrylate, octadecyl acrylate,octadecyl methacrylate, stearyl methacrylate, isobornyl acrylate,tetrahydrofurfuryl acrylate, 2-phenoxyethyl methacrylate, benzylmethacrylate, benzyl acrylate, ethoxylated nonyl phenol methacrylate,ethoxylated behenyl methacrylate, polypropyleneglycol monoacrylate,isobornyl methacrylate, cyclohexyl methacrylate, cyclohexyl acrylate,t-butyl methacrylate, n-octyl methacrylate, lauryl methacrylate,tridecyl methacrylate, alkoxylated tetrahydrofurfuryl acrylate, isodecylacrylate, isobornyl methacrylate, isobornyl acrylate, acetoacetoxyethylmethacrylate, or combinations thereof.

The latex polymer particles can comprise 2-phenoxyethyl methacrylate,cyclohexyl methacrylate, cyclohexyl acrylate, methacrylic acid, orcombinations thereof.

The latex polymer particles can comprise styrene, methyl methacrylate,butyl acrylate, methacrylic acid, or combinations thereof.

The latex polymer particles can be present in the second fluid in anamount ranging from about 5 wt % to about 40 wt % based on the totalweight of the second fluid.

The first liquid vehicle and the second liquid vehicle can comprisewater each in an amount of from about 45 wt % to about 75 wt % based onthe total weight of the first liquid vehicle and the second liquidvehicle, respectively.

The metal nanoparticles can comprise, nickel, silver, gold, copper,platinum, or combinations thereof.

The metal oxide nanoparticles can comprise oxides of iron, nickel,silver, gold, copper, platinum, cobalt, manganese, vanadium, molybdenum,or combinations thereof.

The reducing agent can be selected from the group consisting ofaldehydes, hydrazides, hydrazine, ascorbic acid, reducing saccharides,or combinations thereof.

Single Fluid Kits

In the examples disclosed herein, is a kit for three-dimensionalprinting. The kit can comprise powdered metal build material; and abinding fluid comprising a liquid vehicle, metal or metal precursorparticles, and latex polymer particles dispersed in the liquid vehicle,wherein the latex polymer particles have an average particle size offrom about 10 nm to about 300 nm, and wherein the metal or metalprecursor particles comprise metal nanoparticles, metal oxidenanoparticles, metal oxide nanoparticles and a reducing agent, orcombinations thereof.

The latex polymer particles can be made from (A) a co-polymerizablesurfactant chosen from polyoxyethylene alkylphenyl ether ammoniumsulfate, sodium polyoxyethylene alkylether sulfuric ester,polyoxyethylene styrenated phenyl ether ammonium sulfate, or mixturesthereof, and (B) styrene, p-methyl styrene, α-methyl styrene,methacrylic acid, acrylic acid, acrylamide, methacrylamide,2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropylacrylate, 2-hydroxypropyl methacrylate, methyl methacrylate, hexylacrylate, hexyl methacrylate, butyl acrylate, butyl methacrylate, ethylacrylate, ethyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexylmethacrylate, propyl acrylate, propyl methacrylate, octadecyl acrylate,octadecyl methacrylate, stearyl methacrylate, isobornyl acrylate,tetrahydrofurfuryl acrylate, 2-phenoxyethyl methacrylate, benzylmethacrylate, benzyl acrylate, ethoxylated nonyl phenol methacrylate,ethoxylated behenyl methacrylate, polypropyleneglycol monoacrylate,isobornyl methacrylate, cyclohexyl methacrylate, cyclohexyl acrylate,t-butyl methacrylate, n-octyl methacrylate, lauryl methacrylate,tridecyl methacrylate, alkoxylated tetrahydrofurfuryl acrylate, isodecylacrylate, isobornyl methacrylate, isobornyl acrylate, acetoacetoxyethylmethacrylate, or combinations thereof.

The latex polymer particles can comprise 2-phenoxyethyl methacrylate,cyclohexyl methacrylate, cyclohexyl acrylate, methacrylic acid, orcombinations thereof.

The latex polymer particles can comprise styrene, methyl methacrylate,butyl acrylate, methacrylic acid, or combinations thereof.

The powered metal build material can comprise steels, bronzes, titaniumand alloys thereof, aluminum and alloys thereof, nickel and alloysthereof, cobalt and alloys thereof, iron and alloys thereof, nickelcobalt alloys, gold and alloys thereof, silver and alloys thereof,platinum and alloys thereof, copper and alloys thereof, or combinationsthereof.

The metal nanoparticles can comprise nickel, silver, gold, copper,platinum, or combinations thereof.

The metal oxide nanoparticles can comprise oxides of iron, nickel,silver, gold, copper, platinum, cobalt, manganese, vanadium, molybdenum,or combinations thereof.

The reducing agent is selected from the group consisting of aldehydes,hydrazides, hydrazine, ascorbic acid, reducing saccharides, orcombinations thereof.

The latex polymer particles can be present in the binding fluid in anamount ranging from about 5 wt % to about 40 wt % based on the totalweight of the binding fluid.

3D Printing Methods Multi-Fluid Methods

In the examples disclosed herein, a method of printing athree-dimensional object is described. The method can comprise (i)depositing a metal powder build material in a powder bed; (ii) based ona three-dimensional object model, selectively applying a first fluid anda second fluid on the metal powder build material in the powder bed,wherein the first fluid comprises a first liquid vehicle comprisingmetal or metal precursor particles, wherein the metal or metal precursorparticles comprise metal nanoparticles, metal oxide nanoparticles, metaloxide nanoparticles and a reducing agent, or combinations thereof, andthe second fluid comprises a second liquid vehicle comprising latexpolymer particles dispersed therein, wherein the latex polymer particleshave an average particle size of from about 10 nm to about 300 nm;

(iii) repeating (i), and (ii) at least once to form thethree-dimensional object; and (iv) heating the powder bed to atemperature of up to about 200° C.

The method can further comprise (v) removing the three-dimensionalobject from the powder bed and heating the three-dimensional object to atemperature of up to about 500° C.

The heating to the temperature of up to about 500° C. can compriseremoving at least about 95 wt % of the latex polymer particles bythermally decomposing the latex polymer particles and initiate bindingof metal powder particles with the metal or metal precursor particles.

The latex polymer particles can be present in the second fluid in anamount ranging from about 1 wt % to about 50 wt % based on the totalweight of the second fluid.

The method can further comprise (vi) heating the three-dimensionalobject in a sintering oven to a sintering temperature of greater thanabout 500° C.

Single Fluid Methods

In the examples disclosed herein, a method of printing athree-dimensional object is disclosed. The method can comprise (i)depositing a metal powder build material in a powder bed; (ii) based ona three-dimensional object model, selectively applying a binding fluidon the metal powder build material in the powder bed, wherein thebinding fluid comprises a liquid vehicle, metal or metal precursorparticles, and latex polymer particles dispersed in the liquid vehicle,wherein the metal or metal precursor particles comprise metalnanoparticles, metal oxide nanoparticles, metal oxide nanoparticles anda reducing agent, or combinations thereof, and wherein the latex polymerparticles have an average particle size of from about 10 nm to about 300nm; (iii) repeating (i) and (ii) at least one time to form thethree-dimensional object; and (iv) heating the powder bed to atemperature of up to about 200° C.

The method can further comprise (v) heating the three-dimensional objectin the powder bed to a temperature of up to about 500° C.

The method can further comprise (vi) heating the three-dimensionalobject to a sintering temperature of greater than about 500° C.

A method of using the single fluid kit can comprise applying thepowdered build material and then the binding fluid in athree-dimensional printing bed.

3D Printing Systems

In the examples disclosed herein, a printing system for printing athree-dimensional object is disclosed. The printing system can comprisea supply of one or more binding fluids; a supply of metal powdered buildmaterial; a build material distributor; a fluid applicator forselectively dispensing the binding fluid; a heat source;

a controller; and a non-transitory computer readable medium havingstored thereon computer executable instructions to cause the controllerto print the three-dimensional object by: utilizing the build materialdistributor and the fluid applicator to iteratively form at least onelayer of powdered metal build material having selective application ofthe binding fluid, and utilizing the heat source to heat the selectivelyapplied binding fluid on the powdered metal build material to form thethree-dimensional object.

The powered metal build material can comprise steels, bronzes, titaniumand alloys thereof, aluminum and alloys thereof, nickel and alloysthereof, cobalt and alloys thereof, iron and alloys thereof, nickelcobalt alloys, gold and alloys thereof, silver and alloys thereof,platinum and alloys thereof, copper and alloys thereof, or combinationsthereof.

In some examples, a first fluid can comprise a first liquid vehiclecomprising metal or metal precursor particles. In some examples, asecond fluid can comprise a second liquid vehicle comprising latexpolymer particles dispersed therein, wherein the latex polymer particleshave an average particle size of from about 10 nm to about 300 nm.

In the multi-fluid examples, the metal or metal precursor particles cancomprise metal nanoparticles, metal oxide nanoparticles, metal oxidenanoparticles and a reducing agent, or combinations thereof.

In the single fluid examples, the metal or metal precursor particles cancomprise metal nanoparticles, metal oxide nanoparticles, metal oxidenanoparticles and a reducing agent, or combinations thereof.

Referring now to FIG. 1, an example of a 3D printing system 10 isdepicted. It is to be understood that the 3D printing system 10 mayinclude additional components and that some of the components describedherein may be removed and/or modified. Furthermore, components of the 3Dprinting system 10 depicted in FIG. 1 may not be drawn to scale andthus, the 3D printing system 10 may have a different size and/orconfiguration other than as shown therein.

The three-dimensional (3D) printing system 10 generally includes asupply 14 of metal powder build material 16; a build materialdistributor 18; a supply of a binder fluid 36; an inkjet applicator 24for selectively dispensing the binder fluid 36 (FIG. 2C); at least oneheat source 32; a controller 28; and a non-transitory computer readablemedium having stored thereon computer executable instructions to causethe controller 28 to: utilize the build material distributor 18 and theinkjet applicator 24 to iteratively form multiple layers 34 (FIG. 2B) ofmetal powder build material 16 which are applied by the build materialdistributor 18 and have received the binder fluid 36, thereby creating apatterned green part 42 (FIG. 2E), and utilize the at least one heatsource 32 to heat the patterned green part 42 creating a cured greenpart 42′. In some examples, the cured green part 42′ is heated creatingan at least substantially polymer-free gray part 48. The at leastsubstantially polymer-free gray part 48 or the cured green part 42′ areheated to a sintering temperature to form a metal part 50.

As shown in FIG. 1, the printing system 10 includes a build areaplatform 12, the build material supply 14 containing metal powder buildmaterial particles 16, and the build material distributor 18.

The build area platform (sometimes referred to as the powder bed in thisapplication) 12 receives the metal powder build material 16 from thebuild material supply 14. The build area platform 12 may be integratedwith the printing system 10 or may be a component that is separatelyinsertable into the printing system 10. For example, the build areaplatform 12 may be a module that is available separately from theprinting system 10. The build area platform 12 that is shown is also oneexample, and could be replaced with another support member, such as aplaten, a fabrication/print bed, a glass plate, or another buildsurface.

The build area platform 12 may be moved in a direction as denoted by thearrow 20, e.g., along the z-axis, so that metal powder build material 16may be delivered to the platform 12 or to a previously formed layer ofmetal powder build material 16 (see FIG. 2D). In an example, when themetal powder build material particles 16 are to be delivered, the buildarea platform 12 may be programmed to advance (e.g., downward) enough sothat the build material distributor 18 can push the metal powder buildmaterial particles 16 onto the platform 12 to form a layer 34 of themetal powder build material 16 thereon (see, e.g., FIGS. 2A and 2B). Thebuild area platform 12 may also be returned to its original position,for example, when a new part is to be built.

The build material supply 14 may be a container, bed, or other surfacethat is to position the metal powder build material particles 16 betweenthe build material distributor 18 and the build area platform 12. Insome examples, the build material supply 14 may include a surface uponwhich the metal powder build material particles 16 may be supplied, forinstance, from a build material source (not shown) located above thebuild material supply 14. Examples of the build material source mayinclude a hopper, an auger conveyer, or the like. Additionally, oralternatively, the build material supply 14 may include a mechanism(e.g., a delivery piston) to provide, e.g., move, the metal powder buildmaterial particles 16 from a storage location to a position to be spreadonto the build area platform 12 or onto a previously formed layer ofmetal powder build material 16.

The build material distributor 18 may be moved in a direction as denotedby the arrow 22, e.g., along the y-axis, over the build material supply14 and across the build area platform 12 to spread a layer of the metalpowder build material 16 over the build area platform 12. The buildmaterial distributor 18 may also be returned to a position adjacent tothe build material supply 14 following the spreading of the metal powderbuild material 16. The build material distributor 18 may be a blade(e.g., a doctor blade), a roller, a combination of a roller and a blade,and/or any other device capable of spreading the metal powder buildmaterial particles 16 over the build area platform 12. For instance, thebuild material distributor 18 may be a counter-rotating roller.

The metal powder build material 16 may be any particulate metallicmaterial. In an example, the metal powder build material 16 may be apowder. In another example, the metal powder build material 16 may havethe ability to sinter into a continuous body to form the metal part 50(see, e.g., FIG. 2F) when heated to the sintering temperature (e.g., atemperature ranging from about 850° C. to about 1400° C.). By“continuous body,” it is meant that the metal powder build materialparticles are merged together to form a single part with little or noporosity and with sufficient mechanical strength to meet therequirements of the desired, final metal part 50.

While an example sintering temperature range is provided, it is to beunderstood that this temperature may vary, depending, in part, upon thecomposition and phase(s) of the metal powder build material 16.

The applicator 24 may be scanned across the build area platform 12 inthe direction indicated by the arrow 26, e.g., along the y-axis. Theapplicator 24 may be, for instance, an inkjet applicator, such as athermal inkjet printhead, a piezoelectric printhead, or combinationsthereof, and may extend a width of the build area platform 12. While theapplicator 24 is shown in FIG. 1 as a single applicator, it is to beunderstood that the applicator 24 may include multiple applicators thatspan the width of the build area platform 12. In some examples, a singleor multiple applicators 24 can be used to apply the single fluid binderor multi-fluid binder.

Additionally, the applicators 24 may be positioned in multipleprintbars. The applicator 24 may also be scanned along the x-axis, forinstance, in configurations in which the applicator 24 does not span thewidth of the build area platform 12 to enable the applicator 24 todeposit the binder fluid 36 over a large area of a layer of the metalpowder build material 16. The applicator 24 may thus be attached to amoving XY stage or a translational carriage (neither of which is shown)that moves the applicator 24 adjacent to the build area platform 12 inorder to deposit the binder fluid 36 in predetermined areas of a layerof the metal powder build material 16 that has been formed on the buildarea platform 12 in accordance with the method(s) disclosed herein. Theapplicator 24 may include a plurality of nozzles (not shown) throughwhich the binder fluid 36 is to be ejected.

The “binder fluid 36” as used herein refers to the single fluid binderor multi-fluid binders.

As discussed above, the multi-fluid binder kit for three-dimensionalprinting comprises a first fluid comprising a first liquid vehiclecomprising metal or metal precursor particles; and a second fluidcomprising a second liquid vehicle comprising latex polymer particlesdispersed therein, wherein the latex polymer particles have an averageparticle size of from about 10 nm to about 300 nm, and wherein the metalor metal precursor particles comprise metal nanoparticles, metal oxidenanoparticles, metal oxide nanoparticles and a reducing agent, orcombinations thereof.

As discussed above, the single-fluid binder for three-dimensionalprinting comprises a binding fluid comprising a liquid vehicle, metal ormetal precursor particles, and latex polymer particles dispersed in theliquid vehicle, wherein the latex polymer particles have an averageparticle size of from about 10 nm to about 300 nm, and wherein the metalor metal precursor particles comprise metal nanoparticles, metal oxidenanoparticles, metal oxide nanoparticles and a reducing agent, orcombinations thereof.

The applicator 24 may deliver drops of the binder fluid 36 at aresolution ranging from about 300 dots per inch (DPI) to about 1200 DPI.In other examples, the applicator 24 may deliver drops of the binderfluid 36 at a higher or lower resolution. The drop velocity may rangefrom about 2 m/s to about 24 m/s and the firing frequency may range fromabout 1 kHz to about 100 kHz. In one example, each drop may be in theorder of about 10 picoliters (pl) per drop, although it is contemplatedthat a higher or lower drop size may be used. For example, the drop sizemay range from about 1 pl to about 400 pl. In some examples, applicator24 is able to deliver variable size drops of the binder fluid 36.

Each of the previously described physical elements may be operativelyconnected to a controller 28 of the printing system 10. The controller28 may control the operations of the build area platform 12, the buildmaterial supply 14, the build material distributor 18, and theapplicator 24. As an example, the controller 28 may control actuators(not shown) to control various operations of the 3D printing system 10components. The controller 28 may be a computing device, asemiconductor-based microprocessor, a central processing unit (CPU), anapplication specific integrated circuit (ASIC), and/or another hardwaredevice. Although not shown, the controller 28 may be connected to the 3Dprinting system 10 components via communication lines.

The controller 28 manipulates and transforms data, which may berepresented as physical (electronic) quantities within the printer'sregisters and memories, in order to control the physical elements tocreate the 3D part 50. As such, the controller 28 is depicted as beingin communication with a data store 30. The data store 30 may includedata pertaining to a 3D part 50 to be printed by the 3D printing system10. The data for the selective delivery of the metal powder buildmaterial particles 16 and/or the binder fluid 36 may be derived from amodel of the 3D part 50 to be formed. For instance, the data may includethe locations on each layer of metal powder build material particles 16that the applicator 24 is to deposit the binder fluid 36. In oneexample, the controller 28 may use the data to control the applicator 24to selectively apply the binder fluid 36. The data store 30 may alsoinclude machine readable instructions (stored on a non-transitorycomputer readable medium) that are to cause the controller 28 to controlthe amount of metal powder build material particles 16 that is suppliedby the build material supply 14, the movement of the build area platform12, the movement of the build material distributor 18, the movement ofthe applicator 24.

As shown in FIG. 1, the printing system 10 may also include a heater 32.In some examples, the heater 32 includes a conventional furnace or oven,a microwave, or devices capable of hybrid heating (i.e., conventionalheating and microwave heating). This type of heater 32 may be used forheating the entire build material cake 44 (see FIG. 2E) after theprinting is finished or for heating the cured green part 42′ or forheating the at least substantially polymer-free gray part 48 after thecured green part 42′ is removed from the build material cake 44 (seeFIG. 2F). In some examples, patterning may take place in the printingsystem 10, and then the build material platform 12 with the patternedgreen part 42 thereon may be detached from the system 10 and placed intothe heater 32 for the various heating stages.

In other examples, the heater 32 may be a conductive heater or aradiative heater (e.g., infrared lamps) that is integrated into thesystem 10. These other types of heaters 32 may be placed below the buildarea platform 12 (e.g., conductive heating from below the platform 12)or may be placed above the build area platform 12 (e.g., radiativeheating of the build material layer surface). Combinations of thesetypes of heating may also be used. These other types of heaters 32 maybe used throughout the 3D printing process. In still other examples, theheater 32 may be a radiative heat source (e.g., a curing lamp) that ispositioned to heat each layer 34 (see FIG. 2C) after the binder fluid 36has been applied thereto. In the example shown in FIG. 1, the heater 32is attached to the side of the applicator 24, which allows for printingand heating in a single pass.

It is to be understood that an example of the method 300 shown in FIG. 3is discussed in detail herein, e.g., in FIGS. 2A-2F and the textcorresponding thereto.

Referring now to FIGS. 2A through 2F, an example of the 3D printingmethod is depicted. Prior to execution of the method or as part of themethod (which could be method 300), the controller 28 may access datastored in the data store 30 pertaining to a 3D part 50 that is to beprinted. The controller 28 may determine the number of layers of metalpowder build material particles 16 that are to be formed, and thelocations at which binder fluid 36 from the applicator 24 is to bedeposited on each of the respective layers.

As shown in FIGS. 2A and 2B, the 3D printing method can include applyingthe metal powder build material 16. In FIG. 2A, the build materialsupply 14 may supply the metal powder build material particles 16 into aposition so that they are ready to be spread onto the build areaplatform 12. In FIG. 2B, the build material distributor 18 may spreadthe supplied metal powder build material particles 16 onto the buildarea platform 12. The controller 28 may execute control build materialsupply instructions to control the build material supply 14 toappropriately position the metal powder build material particles 16, andmay execute control spreader instructions to control the build materialdistributor 18 to spread the supplied metal powder build materialparticles 16 over the build area platform 12 to form a layer 34 of metalpowder build material particles 16 thereon. As shown in FIG. 2B, onelayer 34 of the metal powder build material particles 16 has beenapplied.

The layer 34 has a substantially uniform thickness across the build areaplatform 12. In an example, the thickness of the layer 34 ranges fromabout 30 μm to about 300 μm, although thinner or thicker layers may alsobe used. For example, the thickness of the layer 34 may range from about20 μm to about 500 μm. The layer thickness may be about 2× the particlediameter (as shown in FIG. 2B) at a minimum for finer part definition.In some examples, the layer thickness may be about 1.2× (i.e., 1.2times) the particle diameter.

Referring now to FIG. 2C, the method continues by selectively applyingthe binding fluid (also referred to as binder fluid) 36 on a portion 38of the metal powder build material 16. The binder fluid 36 may bedispensed from one or more applicators 24. The applicator 24 may be athermal inkjet printhead or a piezoelectric printhead, and theselectively applying of the binder fluid 36 may be accomplished by theassociated printing technique. As such, the selectively applying of thebinder fluid 36 may be accomplished by thermal inkjet printing or piezoelectric inkjet printing.

The controller 28 may execute instructions to control the applicator 24(e.g., in the directions indicated by the arrow 26) to deposit thebinder fluid 36 onto predetermined portion(s) 38 of the metal powderbuild material 16 that are to become part of a patterned green part 42and are to ultimately be sintered to form the 3D part 50. The applicator24 may be programmed to receive commands from the controller 28 and todeposit the binder fluid 36 according to a pattern of a cross-sectionfor the layer of the 3D part 50 that is to be formed. As used herein,the cross-section of the layer of the 3D part 50 to be formed refers tothe cross-section that is parallel to the surface of the build areaplatform 12. In the example shown in FIG. 2C, the applicator 24selectively applies the binder fluid 36 on those portion(s) 38 of thelayer 34 that are to be fused to become the first layer of the 3D part50. As an example, if the 3D part that is to be formed is to be shapedlike a cube or cylinder, the binder fluid 36 will be deposited in asquare pattern or a circular pattern (from a top view), respectively, onat least a portion of the layer 34 of the metal powder build materialparticles 16. In the example shown in FIG. 2C, the binder fluid 36 isdeposited in a square pattern on the portion 38 of the layer 34 and noton the portions 40.

The applicator 24 (while one is shown there can be multiple applicators)can apply the binder fluid 36 or the first fluid and the second fluid(not shown) simultaneously, consecutively, or sequentially. When thefirst fluid and the second fluid are applied simultaneously, thecomponents in the fluids can mix in-situ on the metal powder buildmaterial 16. When the first fluid and the second fluid are appliedconsecutively or sequentially, there can be limited to no in-situ mixingof the two fluids on the metal powder build material 16. The consecutiveapplication of the first and second fluids can be carried out in anyorder depending on the desired final properties of the final part.

When the binder fluid 36 is selectively applied in the desiredportion(s) 38, the polymer particles and metal or metal precursorparticles (present in the binder fluid 36) infiltrate theinter-particles spaces among the metal powder build material particles16. The volume of the binder fluid 36 that is applied per unit of metalpowder build material 16 in the patterned portion 38 may be sufficientto fill a major fraction, or most of the porosity existing within thethickness of the portion 38 of the layer 34.

It is to be understood that portions 40 of the metal powder buildmaterial 16 that do not have the binder fluid 36 applied thereto also donot have the polymer particles and metal or metal precursor particlesintroduced thereto. As such, these portions do not become part of thepatterned green part 42 that is ultimately formed.

The processes shown in FIGS. 2A through 2C may be repeated toiteratively build up several patterned layers and to form the patternedgreen part 42 (see FIG. 2E).

FIG. 2D illustrates the initial formation of a second layer of metalpowder build material 16 on the layer 34 patterned with the binder fluid36. In FIG. 2D, following deposition of the binder fluid 36 ontopredetermined portion(s) 38 of the layer 34 of metal powder buildmaterial 16, the controller 28 may execute instructions to cause thebuild area platform 12 to be moved a relatively small distance in thedirection denoted by the arrow 20. In other words, the build areaplatform 12 may be lowered to enable the next layer of metal powderbuild material 16 to be formed. For example, the build material platform12 may be lowered a distance that is equivalent to the height of thelayer 34. In addition, following the lowering of the build area platform12, the controller 28 may control the build material supply 14 to supplyadditional metal powder build material 16 (e.g., through operation of anelevator, an auger, or the like) and the build material distributor 18to form another layer of metal powder build material particles 16 on topof the previously formed layer 34 with the additional metal powder buildmaterial 16. The newly formed layer may be patterned with binder fluid36.

Referring back to FIG. 2C, in another example of the method, the layer34 may be exposed to heating using heater 32 after the binder fluid 36is applied to the layer 34 and before another layer is formed. Theheater 32 may be used for heating layer-by-layer and/or for heating theintermediate part. Heating to form the cured green part may take placeat an activating temperature that is capable of activating (or curing)the polymer particles in the binder fluid 36, but that is not capable ofmelting or sintering the metal powder build material 16. Heating to formthe cured green part may further take place at a curing temperature thatis capable of forming metal connections between the metal or metalprecursor particles in the binder fluid 36.

In some examples, the heater 32 can be a photonic fusing source, suchas, a Xenon (Xe) strobe lamp.

In some examples, the at least one energy source may be a continuouswave discharge lamp including xenon, argon, neon, krypton, sodium vapor,metal halide, or mercury-vapor. In another example, the heater 32 may bean array of pulse lasers, continuous wave lasers, light-emitting diode(LED) lasers, or a combination thereof. In this example, the array mayproduce a uniformly dispersed beam. In still another example, the heater32 may be a flash discharge lamp including xenon or krypton. In stillanother example, the heater 32 may be a tungsten-halogen continuous wavelamp. In yet another example, the heater 32 may be a synchrotron lightsource that emits light having a wavelength above 200 nm.

The heater 32 can be capable of emitting enough energy to fuse the metalpowder build material 16 by flash fusing the polymer particles and themetal or metal precursor particles. When the heater 32 is a single pulselight source, the heater 32 may be capable of delivering from about 0.5J to about 100 J/cm². The amount of energy the heater 32 is capable ofdelivering may be less than 70 J/cm² when the heater 32 is multiplepulse light sources and may be greater than 50 J/cm² when the heater 32is a continuous wave light source.

The activating temperature and the fusing temperature are not capable ofmelting or sintering the metal powder build material 16.

In an example, the activation temperature is about the glass transitiontemperature of the polymer particles. Other examples of suitableactivation temperatures are provided below. In an example, the fusingtemperature can be about 180° C. to about 250° C., or from about 190° C.to about 240° C., or from about 200° C. to about 230° C.

In some examples, the processes shown in FIGS. 2A through 2C (includingthe heating of the layer 34) may be repeated to iteratively build upseveral cured layers (one layer at a time) to produce the cured greenpart 42′. The cured green part 42′ can then be exposed to the processesdescribed in reference to FIG. 2F. In some examples, instead oflayer-by-layer heating to activating and fusing temperatures, the buildmaterial cake or intermediate part 44 is heated to the activating andfusing temperatures.

Repeatedly forming and patterning new layers (without curing each layer)results in the formation of a build material cake or intermediate part44, as shown in FIG. 2E, which includes the patterned green part 42residing within the non-patterned portions 40 of each of the layers 34of metal powder build material 16. The patterned green part 42 is avolume of the build material cake 44 that is filled with the metalpowder build material 16 and the binder fluid 36 within theinter-particle spaces. The remainder of the build material cake 44 ismade up of the non-patterned metal powder build material 16.

As shown in FIG. 2E, the build material cake 44 may be exposed to heator radiation to generate heat, as denoted by the arrows 46. The heatapplied may be sufficient to activate and fuse the particles in thebinder fluid 36, in the patterned green part 42 and to produce astabilized and cured green part 42′. In one example, the heat source 32may be used to apply the heat to the build material cake 44. In theexample shown in FIG. 2E, the build material cake 44 may remain on thebuild area platform 12 while being heated by the heat source 32. Inanother example, the build area platform 12, with the build materialcake 44 thereon, may be detached from the applicator 24 and placed inthe heat source 32.

The activation/curing temperature may depend, in part, on one or moreof: the T_(g) of the polymer particles, the melt viscosity of thepolymer particles, and/or whether and which coalescing solvent is used.In an example, heating to form the cured green part 42′ may take placeat a temperature that is capable of activating (or curing) the binderfluid 36, but that is not capable of sintering the metal powder buildmaterial 16 or of thermally degrading the polymer particles of thebinder fluid 36. In an example, the activation temperature is about theminimum film forming temperature (MFFT) or the glass transitiontemperature of the bulk material of the polymer particles of the binderfluid 36 and below the thermal decomposition temperature of the polymerparticles (i.e., below a temperature threshold at which thermaldecomposition occurs). For a majority of suitable latex-based polymerparticles, the upper limit of the activation/curing temperature rangesfrom about 250° C. to about 270° C. Above this temperature threshold,the polymer particles would chemically degrade into volatile species andleave the patterned green part 42, and thus would stop performing theirfunction. In other examples, the binder fluid 36 activation temperaturemay be greater than the MFFT or the glass transition temperature of thepolymer particles. As an example, the binder fluid activationtemperature may range from about 20° C. to about 200° C. As anotherexample, the binder fluid activation temperature may range from about100° C. to about 200° C. As still another example, the binder fluidactivation temperature may range from about 80° C. to about 200° C. Asstill another example, the binder fluid activation temperature may beabout 90° C.

The length of time at which the heat 46 is applied and the rate at whichthe patterned green part 42 is heated may be dependent, for example, onone or more of: characteristics of the heat or radiation source 32,characteristics of the polymer particles, characteristics of the metalor metal precursor particles, characteristics of the metal powder buildmaterial 16 (e.g., metal type, particle size, or combinations thereof),and/or the characteristics of the 3D part 50 (e.g., wall thickness).

The patterned green part 42 may be heated at the binder fluid activationtemperature for an activation and fusing time period ranging from about1 minute to about 360 minutes. In an example, the activation/curing timeperiod is 30 minutes. In another example, the activation and fusing timeperiod may range from about 2 minutes to about 240 minutes. Thepatterned green part 42 may be heated to the binder fluid activation andfusing temperature at a rate of about 1° C./minute to about 10°C./minute, although it is contemplated that a slower or faster heatingrate may be used. The heating rate may depend, in part, on one or moreof: the binder fluid 36 used, the size (i.e., thickness and/or area(across the x-y plane)) of the layer 34 of metal powder build material16, and/or the characteristics of the 3D part 50 (e.g., size, wallthickness, or combinations thereof). In an example, patterned green part42 is heated to the binder fluid activation and fusing temperature at arate of about 2.25° C./minute.

Heating to about the MFFT or the glass transition temperature of thepolymer particles causes the polymer particles to coalesce into acontinuous polymer phase among the metal powder build material particles16 of the patterned green part 42. As mentioned above, the coalescingsolvent (when included in the binder fluid 36) plasticizes the polymerparticles and enhances the coalescing of the polymer particles. Thecontinuous polymer phase may act as a heat-activated adhesive betweenthe metal powder build material particles 16 to form the stabilized,cured green part 42′.

Heating to form the cured green part may further take place at a fusingtemperature that is capable of forming metal connections between themetal or metal precursor particles in the binder fluid 36. In anexample, the fusing temperature can be about 180° C. to about 250° C.,or from about 190° C. to about 240° C., or from about 200° C. to about230° C. The metal connections act as an adhesive between the metalpowder build material particles 16 to form the stabilized, cured greenpart 42′.

In some examples, one of the continuous polymer phase or the metalconnections acts as an adhesive between the metal powder build materialparticles 16 to form the stabilized, cured green part 42′. In someexamples, both the continuous polymer phase or the metal connectionsacts as an adhesive between the metal powder build material particles 16to form the stabilized, cured green part 42′.

Heating to form the cured green part 42′ may also result in theevaporation of a significant fraction of the fluid from the patternedgreen part 42. The evaporated fluid may include any of the binder fluidor first and second fluid components. Fluid evaporation may result insome densification, through capillary action, of the cured green part42′.

The stabilized, cured green part 42′ exhibits handleable mechanicaldurability.

The cured green part 42′ may then be extracted from the build materialcake 44. The cured green part 42′ may be extracted by any suitablemeans. In an example, the cured green part 42′ may be extracted bylifting the cured green part 42′ from the unpatterned metal powder buildmaterial particles 16. An extraction tool including a piston and aspring may be used.

When the cured green part 42′ is extracted from the build material cake44, the cured green part 42′ may be removed from the build area platform12 and placed in a heating mechanism. The heating mechanism may be theheater 32.

In some examples, the cured green part 42′ may be cleaned to removeunpatterned metal powder build material particles 16 from its surface.In an example, the cured green part 42′ may be cleaned with a brushand/or an air jet.

After the extraction and/or the cleaning of the cured green part 42′,the cured green part 42′ may be heated to remove the activated polymerparticles (which have coalesced into the continuous polymer phase) toproduce an at least substantially polymer-free gray part 48, as shown inFIG. 2F. In other words, the cured green part 42′ may be heated toremove the continuous polymer phase. However, the metal or metalprecursor particles remain in the polymer-free gray part 48. Then, theat least substantially polymer-free gray part 48 may be sintered to formthe final 3D part 50, also as shown in FIG. 2F. Heating to de-bind andheating to sinter take place at two different temperatures, where thetemperature for de-binding is lower than the temperature for sintering.Both the de-binding and the sintering heating stages are generallydepicted in FIG. 2F, where heat or radiation to generate heat may beapplied as denoted by the arrows 46 from the heat source 32.

In an example, the thermal decomposition temperature ranges from about250° C. to about 600° C. In another example, the thermal decompositiontemperature ranges from about 280° C. to about 600° C., or to about 500°C. The continuous polymer phase may have a clean thermal decompositionmechanism (e.g., leaves <5 wt % solid residue of the initial binder, andin some instances <1 wt % solid residue of the initial binder). Thesmaller residue percentage (e.g., close to 0%) is more desirable. Duringthe de-binding stage, the long chains of the continuous polymer phasedecompose first intro shorter molecular fragments, which turn into aliquid phase of lower viscosity. Capillary pressure developing duringevaporation of this liquid pulls the metal powder build materialparticles 16 together leading to further densification and formation ofthe at least substantially polymer-free gray part 48.

While not being bound to any theory, it is believed that the at leastsubstantially polymer-free gray part 48 may maintain its shape due, forexample, to one or more of: i) the low amount of stress experienced bythe at least substantially polymer-free gray part 48 due to it not beingphysically handled, ii) low level necking occurring between the metalpowder build material particles 16 and the polymer particles and metalor metal precursor particles, and/or iii) capillary forces pushing themetal powder build material particles 16 together generated by theremoval of the continuous polymer phase. The at least substantiallypolymer-free gray part 48 may maintain its shape although the continuouspolymer phase is at least substantially removed and the metal powderbuild material particles 16 is not yet sintered at least because of themetal connections between the metal or metal precursor particles in theinterstitial spaces between the powder build material particles 16.

Heating to sinter is accomplished at a sintering temperature that issufficient to sinter the remaining metal powder build material particles16. The sintering temperature is dependent upon the composition of themetal powder build material particles 16. During heating/sintering, theat least substantially polymer-free gray part 48 may be heated to atemperature ranging from about 80% to about 99.9% of the melting pointor the solidus, eutectic, or peritectic temperature of the metal powderbuild material 16. In another example, the at least substantiallypolymer-free gray part 48 may be heated to a temperature ranging fromabout 90% to about 95% of the melting point or the solidus, eutectic, orperitectic temperature of the metal powder build material 16. In stillanother example, the at least substantially polymer-free gray part 48may be heated to a temperature ranging from about 60% to about 85% ofthe melting point or the solidus, eutectic, or peritectic temperature ofthe metal powder build material 16. The sintering heating temperaturemay also depend upon the particle size and time for sintering (i.e.,high temperature exposure time).

As an example, the sintering temperature may range from about 850° C. toabout 1400° C. In another example, the sintering temperature is at least900° C. An example of a sintering temperature for bronze is about 850°C., and an example of a sintering temperature for stainless steel isbetween about 1200° C. and 1500° C. While these temperatures areprovided as sintering temperature examples, it is to be understood thatthe sintering heating temperature depends upon the metal powder buildmaterial 16 that is utilized. Heating at a suitable temperature sintersand fuses the metal powder build material particles 16 to form acompleted 3D part 50, which may be even further densified relative tothe at least substantially polymer-free gray part 48. For example, as aresult of sintering, the density may go from 50% density to over 90%,and in some cases very close to 100% of the theoretical density.

During sintering, the metal or metal precursor particles (metalnanoparticles) may adjust shape and diffuse between the metal powderbuild material particles 16 allowing formation of strong mechanicalconnections. The sintering process can improve adhesion between themetal nanoparticles and the metal powder build material particles 16.Sintering can also be used to increase the density of the part. Forexample, small voids in the polymer-free gray part 48 may be filled withdiffusing metal nanoparticles during sintering. Diffusion sinteringregimes and remodeling sintering regimes are within the knowledge of theskilled practitioner and useful texts are available to provide guidanceand models for such operations, for example: Randall German, 1994, MetalPowder Industries Federation, Princeton, N.J.

The length of time at which the heat 46 (for each of de-binding andsintering) is applied and the rate at which the part 42′, 48 is heatedmay be dependent, for example, on one or more of: characteristics of theheat or radiation source 32, characteristics of the polymer particles,characteristics of the metal nanoparticles, characteristics of the metalpowder build material 16 (e.g., metal type, particle size, orcombinations thereof), and/or the characteristics of the 3D part 50(e.g., wall thickness).

The cured green part 42′ may be heated at the thermal decompositiontemperature for a thermal decomposition time period ranging from about10 minutes to about 72 hours. In an example, the thermal decompositiontime period is 60 minutes. In another example, thermal decompositiontime period is 180 minutes. The cured green part 42′ may be heated tothe thermal decomposition temperature at a rate ranging from about 0.5°C./minute to about 20° C./minute. The heating rate may depend, in part,on one or more of: the amount of the continuous polymer phase in thecured green part 42′, the porosity of the cured green part 42′, and/orthe characteristics of the cured green part 42′/3D part 50 (e.g., size,wall thickness, or combinations thereof).

The at least substantially polymer-free gray part 48 may be heated atthe sintering temperature for a sintering time period ranging from about20 minutes to about 15 hours. In an example, the sintering time periodis 240 minutes. In another example, the sintering time period is 360minutes. The at least substantially polymer-free gray part 48 may beheated to the sintering temperature at a rate ranging from about 1°C./minute to about 20° C./minute. In an example, the at leastsubstantially polymer-free gray part 48 is heated to the sinteringtemperature at a rate ranging from about 10° C./minute to about 20°C./minute. A high ramp rate up to the sintering temperature may bedesirable to produce a more favorable grain structure or microstructure.However, in some instances, slower ramp rates may be desirable. As such,in another example, the at least substantially polymer-free gray part 48is heated to the sintering temperature at a rate ranging from about 1°C./minute to about 3° C./minute. In yet another example, the at leastsubstantially polymer-free gray part 48 is heated to the sinteringtemperature at a rate of about 1.2° C./minute. In still another example,the at least substantially polymer-free gray part 48 is heated to thesintering temperature at a rate of about 2.5° C./minute.

In example of the method: the heating of the cured green part 42′ to thethermal decomposition temperature is performed for a thermaldecomposition time period ranging from about 30 minutes to about 72hours; and the heating of the at least substantially polymer-free graypart 48 to the sintering temperature is performed for a sintering timeperiod ranging from about 20 minutes to about 15 hours. In anotherexample of the method: the heating of the cured green part 42′ to thethermal decomposition temperature is accomplished at a rate ranging fromabout 0.5° C./minute to about 10° C./minute; and the heating of the atleast substantially polymer-free gray part 48 to the sinteringtemperature is accomplished at a rate ranging from about 1° C./minute toabout 20° C./minute.

In some examples of the method, the heat 46 (for each of de-binding andsintering) is applied in an environment containing an inert gas, a lowreactivity gas, a reducing gas, or a combination thereof. In otherwords, the heating of the cured green part 42′ to the thermaldecomposition temperature and the heating of the at least substantiallypolymer-free gray part 48 to the sintering temperature are accomplishedin an environment containing an inert gas, a low reactivity gas, areducing gas, or a combination thereof. The de-binding may beaccomplished in an environment containing an inert gas, a low reactivitygas, and/or a reducing gas so that the continuous polymer phasethermally decomposes rather than undergo an alternate reaction whichwould fail to produce the at least substantially polymer-free gray part48 and/or to prevent the oxidation of the metal powder build material16. The sintering may be accomplished in an environment containing aninert gas, a low reactivity gas, and/or a reducing gas so that the metalpowder build material 16 will sinter rather than undergoing an alternatereaction (e.g., an oxidation reaction) which would fail to produce themetal 3D part 50. Examples of inert gas include argon, helium, or othersimilar noble inert gases. An example of a low reactivity gas includesnitrogen and examples of reducing gases include hydrogen, carbonmonoxide, or a mixture thereof.

In other examples of the method, the heat 46 (for each of de-binding(i.e., heating of the cured green body 42′ to the thermal decompositiontemperature) and sintering (i.e., heating of the at least substantiallypolymer free grey part to the sintering temperature)) is applied in anenvironment containing carbon in addition to an inert gas, a lowreactivity gas, a reducing gas, or a combination thereof. The de-bindingand the sintering may be accomplished in an environment containingcarbon to reduce the partial pressure of oxygen in the environment andfurther prevent the oxidation of the metal powder build material 16during de-binding and sintering. An example of the carbon that may beplaced in the heating environment includes graphite rods. In otherexamples, a graphite furnace may be used.

In still other examples of the method, the heat 46 (for each ofde-binding and sintering) is applied in a low gas pressure or vacuumenvironment. The de-binding and the sintering may be accomplished in alow gas pressure or vacuum environment so that the continuous polymerphase thermally decomposes and/or to prevent the oxidation of the metalpowder build material 16. Moreover, sintering at the low gas pressure orunder vacuum may allow for more complete or faster pore collapse, andthus higher density parts. However, vacuum may not be used duringsintering when the metal powder build material 16 (e.g., Cr) is capableof evaporating in such conditions. In an example, the low pressureenvironment is at a pressure ranging from about 1E-5 torr (1*10⁻⁵ torr)to about 10 torr.

Although not shown, the operations depicted in FIGS. 2E and 2F may beautomated and the controller 28 may control the operations.

In FIG. 3, a flow diagram shows a method of printing a three-dimensionalobject (300) comprising: (i) depositing a metal powder build material ina powder bed (310); (ii) based on a three-dimensional object model,selectively applying a first fluid and a second fluid on the metalpowder build material in the powder bed (320), wherein the first fluidcomprises a first liquid vehicle comprising metal or metal precursorparticles, wherein the metal or metal precursor particles comprise metalnanoparticles, metal oxide nanoparticles, metal oxide nanoparticles anda first reducing agent, metal salts, metal salts with a second reducingagent, or combinations thereof, and the second fluid comprises a secondliquid vehicle comprising latex polymer particles dispersed therein,wherein the latex polymer particles have an average particle size offrom about 10 nm to about 300 nm; (iii) repeating (i), and (ii) at leastonce to form the three-dimensional object (330); and (iv) heating thepowder bed to a temperature of up to about 200° C. (340).

Metal Powder Build Material

In an example, the metal powder build material 16 is a single phasemetal material composed of one element. In this example, the sinteringtemperature may be below the melting point of the single element.

In another example, the metal powder build material 16 is composed oftwo or more elements, which may be in the form of a single phase metalalloy or a multiple phase metal alloy. In these other examples, meltinggenerally occurs over a range of temperatures. For some single phasemetal alloys, melting begins just above the solidus temperature (wheremelting is initiated) and is not complete until the liquidus temperature(temperature at which all the solid has melted) is exceeded. For othersingle phase metal alloys, melting begins just above the peritectictemperature. The peritectic temperature is defined by the point where asingle phase solid transforms into a two phase solid plus liquidmixture, where the solid above the peritectic temperature is of adifferent phase than the solid below the peritectic temperature. Whenthe metal powder build material 16 is composed of two or more phases(e.g., a multiphase alloy made of two or more elements), meltinggenerally begins when the eutectic or peritectic temperature isexceeded. The eutectic temperature is defined by the temperature atwhich a single phase liquid completely solidifies into a two phasesolid. Generally, melting of the single phase metal alloy or themultiple phase metal alloy begins just above the solidus, eutectic, orperitectic temperature and is not complete until the liquidustemperature is exceeded. In some examples, sintering can occur below thesolidus temperature, the peritectic temperature, or the eutectictemperature. In other examples, sintering occurs above the solidustemperature, the peritectic temperature, or the eutectic temperature.Sintering above the solidus temperature is known as super solidussintering, and this technique may be desirable when using larger buildmaterial particles and/or to achieve high density. In an example, thebuild material composition may be selected so that at least 40 vol % ofthe metal powder build material is made up of phase(s) that have amelting point above the desired sintering temperature. It is to beunderstood that the sintering temperature may be high enough to providesufficient energy to allow atom mobility between adjacent particles.

Single elements or alloys may be used as the metal powder build material16. Some examples of the metal powder build material 16 include steels,stainless steel, bronzes, titanium (Ti) and alloys thereof, aluminum(Al) and alloys thereof, nickel (Ni) and alloys thereof, cobalt (Co) andalloys thereof, iron (Fe) and alloys thereof, nickel cobalt (NiCo)alloys, gold (Au) and alloys thereof, silver (Ag) and alloys thereof,platinum (Pt) and alloys thereof, and copper (Cu) and alloys thereof.Some specific examples include AlSi10Mg, 2xxx series aluminum, 4xxxseries aluminum, CoCr MP1, CoCr SP2, MaragingSteel MS1, Hastelloy C,Hastelloy X, NickelAlloy HX, Inconel IN625, Inconel IN718, SS GP1, SS17-4PH, SS 316L, Ti6Al4V, and Ti-6Al-4V EL17. While several examplealloys have been provided, it is to be understood that other alloy buildmaterials may be used, such as PbSn soldering alloys.

Any metal powder build material 16 may be used that is in powder form atthe outset of the 3D printing method(s) disclosed herein. As such, themelting point, solidus temperature, eutectic temperature, and/orperitectic temperature of the metal powder build material 16 may beabove the temperature of the environment in which the patterning portionof the 3D printing method is performed (e.g., above 40° C.). In someexamples, the metal powder build material 16 may have a melting pointranging from about 850° C. to about 3500° C. In other examples, themetal powder build material 16 may be an alloy having a range of meltingpoints. Alloys may include metals with melting points as low as −39° C.(e.g., mercury), or 30° C. (e.g., gallium), or 157° C. (indium), orcombinations thereof.

The metal powder build material 16 may be made up of similarly sizedparticles or differently sized particles. In the examples shown herein(FIG. 1 and FIGS. 2A-2F), the metal powder build material 16 includessimilarly sized particles. The term “size”, as used herein with regardto the metal powder build material 16, refers to the diameter of asubstantially spherical particle (i.e., a spherical or near-sphericalparticle having a sphericity of >0.84), or the average diameter of anon-spherical particle (i.e., the average of multiple diameters acrossthe particle). Substantially spherical particles of this particle sizehave good flowability and can be spread relatively easily. As anexample, the average particle size of the particles of the metal powderbuild material 16 may range from about 1 μm to about 200 μm. As anotherexample, the average size of the particles of the metal powder buildmaterial 16 ranges from about 10 μm to about 150 μm. As still anotherexample, the average size of the particles of the metal powder buildmaterial 16 ranges from 15 μm to about 100 μm.

Binder Fluid or First Fluid and Second Fluid

As shown in FIG. 1, the printing system 10 also includes an applicator24, which may contain the binder fluid 36 (shown in FIG. 2C) disclosedherein. In some examples, the binder fluid 36 (also referred to hereinas the binding fluid 36) can be created, stored, and applied as twoseparate fluids—a first fluid and a second fluid. As discussed above,the first fluid can comprise a first liquid vehicle comprising metal ormetal precursor particles and the second fluid can comprise a secondliquid vehicle comprising latex polymer particles dispersed therein. Thelatex polymer particles have an average particle size of from about 10nm to about 300 nm and the metal or metal precursor particles comprisemetal nanoparticles, metal oxide nanoparticles, metal oxidenanoparticles and a reducing agent, or combinations thereof.

While not shown in FIG. 2C, the binder fluid 36 can be one single fluidor two separate fluids—the first fluid and the second fluid, whichis/are ejected from one or more applicators 24 (only one applicatorshown) onto the metal powder build material 16.

The binder fluid 36 includes at least the liquid vehicle, the polymerparticles, and the metal or metal precursor particles. In someinstances, the binder fluid 36 consists of the liquid vehicle, thepolymer particles, and the metal or metal precursor particles, withoutany other components.

In some examples, the binding fluid (also referred to as the binderfluid herein) has a pH of from about 6.5 to about 9, or less than about8.5, or less than about 8, or less than about 7.5, or at least about6.8, or at least about 6.9, or at least about 7, or at least about 7.5.

In some examples, the viscosity of the binding fluid composition is lessthan about 10 cps, or less than about 15 cps, or less than about 14 cps,or less than about 13 cps, or less than about 12 cps, or less than about11 cps, or less than about 10 cps, or less than about 9 cps, or lessthan about 8 cps, or less than about 7 cps, or less than about 6 cps, orless than about 5 cps, or less than about 4 cps, or less than about 3cps.

In some examples, the first fluid can comprise a first liquid vehiclecomprising metal or metal precursor particles with no other componentsand the second fluid can comprise a second liquid vehicle comprisinglatex polymer particles dispersed therein with no other components.

All liquid vehicles described herein—in the binding fluid 36, in thefirst fluid and in the second fluid—can all be the same or similar. ThepH of the first fluid and the second fluid can be from about 6.5 toabout 9, or less than about 8.5, or less than about 8, or less thanabout 7.5, or at least about 6.8, or at least about 6.9, or at leastabout 7, or at least about 7.5. The viscosity of the first fluid and thesecond fluid can be less than about 10 cps, or less than about 15 cps,or less than about 14 cps, or less than about 13 cps, or less than about12 cps, or less than about 11 cps, or less than about 10 cps, or lessthan about 9 cps, or less than about 8 cps, or less than about 7 cps, orless than about 6 cps, or less than about 5 cps, or less than about 4cps, or less than about 3 cps.

Polymer Particles

In the examples disclosed herein, the polymer particles may be dispersedin the liquid vehicle. The polymer particles may have anymorphology—e.g., single-phase, or core-shell, partially occluded,multiple-lobed, or combinations thereof.

In one example, the polymer particles may be made of two differentcopolymer compositions. These might be fully separated “core-shell”polymers, partially occluded mixtures, or intimately comingled as a“polymer solution.” In another example, the polymer particle morphologymay resemble a raspberry, in which a hydrophobic core is surrounded by alarge number of smaller hydrophilic particles that are attached to thecore. In still another example, the polymer particles may include 2, 3,4, or more relatively large particle “lobes” surrounding a smallerpolymer core.

The polymer particles may be any latex polymer (i.e., polymer that iscapable of being dispersed in an aqueous medium) that is jettable viainkjet printing (e.g., thermal inkjet printing or piezoelectric inkjetprinting). In some examples disclosed herein, the polymer particles areheteropolymers or co-polymers. The heteropolymers may include a morehydrophobic component and a more hydrophilic component. In theseexamples, the hydrophilic component renders the particles dispersible inthe binder fluid 36, while the hydrophobic component is capable ofcoalescing upon exposure to heat in order to temporarily bind the metalpowder build material particles 16 together to form the cured green part42′.

Examples of low T_(g) monomers that may be used to form the hydrophobiccomponent include C4 to C8 alkyl acrylates or methacrylates, styrene,substituted methyl styrenes, polyol acrylates or methacrylates, vinylmonomers, vinyl esters, or the like. Some specific examples includemethyl methacrylate, butyl acrylate, butyl methacrylate, hexyl acrylate,hexyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate,propyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexy methacrylate,hydroxyethyl acrylate, lauryl acrylate, lauryl methacrylate, octadecylacrylate, octadecyl methacrylate, isobornyl acrylate, isobornylmethacrylate, stearyl methacrylate, ethylene glycol dimethacrylate,diethylene glycol dimethacrylate, triethylene glycol dimethacrylate,tetrahydrofurfuryl acrylate, alkoxylated tetrahydrofurfuryl acrylate,2-phenoxyethyl methacrylate, benzyl acrylate, ethoxylated nonyl phenolmethacrylate, cyclohexyl methacrylate, trimethyl cyclohexylmethacrylate, t-butyl methacrylate, n-octyl methacrylate, trydecylmethacrylate, isodecyl acrylate, dimethyl maleate, dioctyl maleate,acetoacetoxyethyl methacrylate, diacetone acrylamide, pentaerythritoltri-acrylate, pentaerythritol tetra-acrylate, pentaerythritoltri-methacrylate, pentaerythritol tetra-methacrylate, divinylbenzene,styrene, methylstyrenes (e.g., a-methyl styrene, p-methyl styrene),vinyl chloride, vinylidene chloride, vinylbenzyl chloride,acrylonitrile, methacrylonitrile, N-vinyl imidazole, N-vinylcarbazole,N-vinyl-caprolactam, combinations thereof, derivatives thereof, ormixtures thereof.

Examples of monomers that can be used in forming the polymer particlesinclude acrylic acid, methacrylic acid, ethacrylic acid, dimethylacrylicacid, maleic anhydride, maleic acid, vinylsulfonate, cyanoacrylic acid,vinylacetic acid, allylacetic acid, ethylidineacetic acid,propylidineacetic acid, crotonoic acid, fumaric acid, itaconic acid,sorbic acid, angelic acid, cinnamic acid, styrylacrylic acid, citraconicacid, glutaconic acid, aconitic acid, phenylacrylic acid,acryloxypropionic acid, aconitic acid, phenylacrylic acid,acryloxypropionic acid, vinylbenzoic acid, N-vinylsuccinamidic acid,mesaconic acid, methacroylalanine, acryloylhydroxyglycine, sulfoethylmethacrylic acid, sulfopropyl acrylic acid, styrene sulfonic acid,sulfoethylacrylic acid, 2-methacryloyloxymethane-1-sulfonic acid,3-methacryoyloxypropane-1-sulfonic acid, 3-(vinyloxy)propane-1-sulfonicacid, ethylenesulfonic acid, vinyl sulfuric acid, 4-vinylphenyl sulfuricacid, ethylene phosphonic acid, vinyl phosphoric acid, vinyl benzoicacid, 2 acrylamido-2-methyl-1-propanesulfonic acid, combinationsthereof, derivatives thereof, or mixtures thereof. Other examples ofhigh T_(g) hydrophilic monomers include acrylamide, methacrylamide,monohydroxylated monomers, monoethoxylated monomers, polyhydroxylatedmonomers, or polyethoxylated monomers.

In an example, the selected monomer(s) is/are polymerized to form apolymer, heteropolymer, or copolymer. In some examples, the monomer(s)are polymerized with a co-polymerizable surfactant. In some examples,the co-polymerizable surfactant can be a polyoxyethylene compound. Insome examples, the co-polymerizable surfactant can be a Hitenol®compound e.g., polyoxyethylene alkylphenyl ether ammonium sulfate,sodium polyoxyethylene alkylether sulfuric ester, polyoxyethylenestyrenated phenyl ether ammonium sulfate, or mixtures thereof. Anysuitable polymerization process may be used. The polymer particles mayhave a particle size that can be jetted via thermal inkjet printing orpiezoelectric printing or continuous inkjet printing. In an example, theparticle size of the polymer particles ranges from about 10 nm to about300 nm.

In some examples, the polymer particles have a MFFT or a glasstransition temperature (T_(g)) that is greater (e.g., >) than ambienttemperature. In other examples, the polymer particles have a MFFT orglass transition temperature (T_(g)) that is much greater (e.g., >>)than ambient temperature (i.e., at least 15° higher than ambient). Asused therein, “ambient temperature” may refer to room temperature (e.g.,ranging about 18° C. to about 22° C.), or to the temperature of theenvironment in which the 3D printing method is performed. Examples ofthe 3D printing environment ambient temperature may range from about 40°C. to about 50° C. The MFFT or the glass transition temperature T_(g) ofthe bulk material (e.g., the more hydrophobic portion) of the polymerparticles may range from 25° C. to about 125° C. In an example, the MFFTor the glass transition temperature T_(g) of the bulk material (e.g.,the more hydrophobic portion) of the polymer particles is about 40° C.or higher. The MFFT or the glass transition temperature T_(g) of thebulk material may be any temperature that enables the polymer particlesto be inkjet printed without becoming too soft at the printer operatingtemperatures.

The polymer particles may have a MFFT or glass transition temperatureranging from about 125° C. to about 200° C. In an example, the polymerparticles may have a MFFT or glass transition temperature of about 160°C.

The weight average molecular weight of the polymer particles may rangefrom about 10,000 Mw to about 500,000 Mw. In some examples, the weightaverage molecular weight of the polymer particles ranges from about100,000 Mw to about 500,000 Mw. In some other examples, the weightaverage molecular weight of the polymer particles ranges from about150,000 Mw to 300,000 Mw.

When each of the polymer particles contains a low T_(g) hydrophobiccomponent and a high T_(g) hydrophilic component, the polymer particlesmay be prepared by any suitable method. As examples, the polymerparticles may be prepared by one of the following methods.

In an example, the polymer particles may be prepared by polymerizinghigh T_(g) hydrophilic monomers to form the high T_(g) hydrophiliccomponent and attaching the high T_(g) hydrophilic component onto thesurface of the low T_(g) hydrophobic component.

In another example, each of the polymer particles may be prepared bypolymerizing the low T_(g) hydrophobic monomers and the high T_(g)hydrophilic monomers at a ratio of the low T_(g) hydrophobic monomers tothe high T_(g) hydrophilic monomers that ranges from 5:95 to 30:70. Inthis example, the soft low T_(g) hydrophobic monomers may dissolve inthe hard high T_(g) hydrophilic monomers.

In still another example, each of the polymer particles may be preparedby starting the polymerization process with the low T_(g) hydrophobicmonomers, then adding the high T_(g) hydrophilic monomers, and thenfinishing the polymerization process. In this example, thepolymerization process may cause a higher concentration of the highT_(g) hydrophilic monomers to polymerize at or near the surface of thelow T_(g) hydrophobic component.

In still another example, each of the polymer particles may be preparedby starting a copolymerization process with the low T_(g) hydrophobicmonomers and the high T_(g) hydrophilic monomers, then adding additionalhigh T_(g) hydrophilic monomers, and then finishing the copolymerizationprocess. In this example, the copolymerization process may cause ahigher concentration of the high T_(g) hydrophilic monomers tocopolymerize at or near the surface of the low T_(g) hydrophobiccomponent.

The low T_(g) hydrophobic monomers and/or the high T_(g) hydrophilicmonomers used in any of these examples may be any of the low T_(g)hydrophobic monomers and/or the high T_(g) hydrophilic monomers(respectively) listed above. In an example, the low T_(g) hydrophobicmonomers are selected from the group consisting of C4 to C8 alkylacrylate monomers, C4 to C8 alkyl methacrylate monomers, styrenemonomers, substituted methyl styrene monomers, vinyl monomers, vinylester monomers, and combinations thereof; and the high T_(g) hydrophilicmonomers are selected from the group consisting of acidic monomers,unsubstituted amide monomers, alcoholic acrylate monomers, alcoholicmethacrylate monomers, C1 to C2 alkyl acrylate monomers, C1 to C2 alkylmethacrylate monomers, and combinations thereof.

The resulting polymer particles may exhibit a core-shell structure, amixed or intermingled polymeric structure, or some other morphology.

The polymer particles may be present in the binder fluid 36 in an amountranging from about 2 wt % to about 50 wt %, or from about 3 wt % toabout 40 wt %, or from about 5 wt % to about 30 wt %, or from about 10wt % to about 20 wt %, or from about 12 wt % to about 18 wt %, or about15 wt % (based upon the total wt % of the binder fluid 36). In anotherexample, the polymer particles may be present in the binder fluid 36 inan amount ranging from about 20 vol % to about 40 vol % (based upon thetotal vol % of the binder fluid 36). It is believed that these polymerparticle loadings provide a balance between the binder fluid 36 havingjetting reliability and binding efficiency. In an example, the polymerparticles are present in the binder fluid in an amount ranging fromabout 2 wt % to about 30 wt %, and the coalescing solvent is present inthe binder fluid in an amount ranging from about 0.1 wt % to about 50 wt%.

In an example, the latex polymer particles have an average particle sizeof from about 10 nm to about 300 nm, or from about 50 nm to about 300nm, or from about 100 nm to about 300 nm, or from about 110 nm to about300 nm, from about 120 nm to about 300 nm, or from about 130 nm to about300 nm, or from about 140 nm to about 300 nm, or from about 150 nm toabout 300 nm, or from about 160 nm to about 290 nm, or from about 170 nmto about 300 nm, or from about 180 nm to about 2700 nm, or from about190 nm to about 250 nm, or from about 190 nm to about 230 nm, or fromabout 190 nm to about 220 nm, or from about 190 nm to about 210 nm, orabout 200 nm.

Metal or Metal Precursor Particles

In some examples, the metal or metal precursor particles can comprisemetal nanoparticles, metal oxide nanoparticles, metal oxidenanoparticles and a reducing agent, or combinations thereof.

The metal nanoparticles can comprise, nickel, silver, gold, copper,platinum, or combinations thereof. The metal oxide nanoparticles cancomprise oxides of iron, nickel, silver, gold, copper, platinum, cobalt,manganese, vanadium, molybdenum, or combinations thereof. The reducingagent can be selected from the group consisting of aldehydes,hydrazides, hydrazine, ascorbic acid, reducing saccharides, orcombinations thereof.

The metal or metal precursor particles can encompass a wide range ofshapes, sizes, distributions, and materials. Whatever shape, size,distribution, or material is used, the particles retain their shapeduring the process of applying them to the metal powder material 16 andforming metal connections between the metal powder material particles16. The metal or metal precursor particles may be of any shape. Themetal or metal precursor particles may be formed by processing. Themetal or metal precursor particles may be naturally shaped materials.The metal or metal precursor particles may include a variety ofdifferent shapes. The metal or metal precursor particles may be selectedand/or sorted to have a given geometry. The metal or metal precursorparticles may include flakes, sheets, plates, or similar flattened,primarily two-dimensional geometry. The metal or metal precursorparticles may include rods, spindles, spheres, or blocks. The metal ormetal precursor particles may have a mean and/or median particlediameter of less an about 1000 nm, or less than about 500 nm, or lessthan about 200 nm, or less than about 100 nm, or from about 10 nm toabout 100 nm, or from about 1 μm to about 1000 μm, or from about 10 μmto 500 μm, or from about 50 μm to about 200 μm.

The metal or metal precursor particles used may be of a single sizedistribution. The metal or metal precursor particles may include amixture of multiple size distributions. The metal or metal precursorparticles may all have a similar and/or identical composition.Alternately, several different types of metal or metal precursorparticles may be combined. For example, multiple types of metal or metalprecursor particles can be combined to form an alloy after a secondaryheating operation. Alternately, composition gradients can be formed. Forexample, areas of a part needing ductility may have a higher nickelconcentration. By comparison, nickel concentration may be at a reducedlevel near surfaces that will be in contact with skin. The formation ofstructured/supported electrodes can be formed. For example, a small areaof a noble metal such as platinum or gold can be formed in an area of arefractory metal such as titanium. The refractory metal can be oxidizedin a post-forming process to form an insulator leaving the noble metalarea to act as an electrode. Because both the metal or metal precursorparticles and the deposited metal can be selected and applied with highprecision, a wide variety of non-uniform materials can be readilyformed. Thus, composition gradients in the consolidated part can beformed using variation of the particles, variation of the depositedmetal connections, or both.

In some examples, the metal or metal precursor particles may be formedof a wide variety of materials including, but not limited to: metal,metal oxides, metal carbides, metal nitrides, ceramics, non-metals,metalloids, semiconductors, polymers (especially thermosets butincluding thermoplastic polymers), minerals, carbon black, graphite,diamond, organic materials, or combinations thereof. The metal or metalprecursor particles are stable during the formation of the metalconnections. As this may be accomplished in a variety of ways describedbelow, different materials will be more and/or less suited forparticular approaches. Further, the material selection has a significantimpact on the characteristics of the consolidated part and what kinds ofsecondary processes may be used. Clearly, the particles selected willalso impact the characteristics of a final part.

The metal or metal precursor particles can be formed from a wide varietyof metals. However, the surface of some metals tends to oxidize, formingmetal oxides. In some examples, it is advantageous to coat the metal ormetal precursor particles to prevent or reduce the surface oxidation.The coating may be of a second metal. For example, an iron nanoparticlecould be coated with silver to avoid oxidation. The coating may be apolymer. For example, a nickel nanoparticle could be coated withpolyethylene. The coating may be a suitable organic or inorganic coatingthat reduces and/or prevents the oxidation of the coated metal or metalprecursor particles. In some examples, the coating is designed todecompose or volatilize at temperatures under the melting point of thenanoparticle. This may help prevent the coating from inhibiting adhesionbetween the metal or metal precursor particles and the adjacent metalpowder build material particles 16. In another example, metal oxidecoated nanoparticles are provided with a reducing agent either as partof the particle, as a coating, or applied separately. The reducing agentis activated causing a reduction of the metal oxide and formation ofmetal connections.

The polymer-free grey part 48 with the metal or metal precursorparticles are reorganized within the interstitial spaces of thepolymer-free grey part 48 to form metal connections between the metal ormetal precursor particles. The metal connections preferentially occupyspaces between the metal powder build material particles 16 due to thehigh volume to new surface area ratio provided by those locations.However, not every junction need be connected in order to form a solid,consolidated part. There is a random component to which metal powderbuild material particles 16 get connected together via the metalconnections and which do not. Accordingly, there is a threshold belowwhich the weight percentage of metal or metal precursor particles willnot provide acceptable strength. In some instances, a part with a lowermetal or metal precursor particles loading may be brittle or vulnerableto damage even though it is solid. However, as metal or metal precursorparticles tend to be expensive compared with the metal powder buildmaterial particles 16, there is a tradeoff between mechanical robustnessand the percentage of metal or metal precursor particles used as apercentage of total weight of the part.

Functional parts can be produced with binding fluid compositions orfirst fluid compositions having from about 0.1 wt % to about 15 wt %metal or metal precursor particles by weight of the final part. Higherloadings of metal or metal precursor particles appear to reduce thetemperature needed to obtain consolidation, produce higher densities,and may reduce the shrinkage observed during a subsequentheating/sintering operation. This is consistent with a model where themetal or metal precursor particles are binding the metal powder buildmaterial particles 16 together and filling gaps between the metal powderbuild material particles 16.

Solvent

In some examples, the binder fluid 36, the first fluid, and the secondfluid each include liquid vehicles that each include at least onesolvent.

In some examples, the solvent acts as a coalescing solvent in the binderfluid 36 and in the second fluid when present with the polymer particlesby plasticizing the polymer particles and enhancing the coalescing ofthe polymer particles upon exposure to heat. In some examples, theliquid vehicle may consist of the polymer particles and the coalescingsolvent (with no other components). In these examples, the liquidvehicle consists of the coalescing solvent (with no other components),and the coalescing solvent makes up the balance of the binder fluid 36.

In some examples, the solvent may be lactams, such as 2-pyrrolidinone,1-(2-hydroxyethyl)-2-pyrrolidone, or combinations thereof. In otherexamples, the solvent may be a glycol ether or a glycol ether esters,such as tripropylene glycol mono methyl ether, dipropylene glycol monomethyl ether, dipropylene glycol mono propyl ether, tripropylene glycolmono n-butyl ether, propylene glycol phenyl ether, dipropylene glycolmethyl ether acetate, diethylene glycol mono butyl ether, diethyleneglycol mono hexyl ether, ethylene glycol phenyl ether, diethylene glycolmono n-butyl ether acetate, ethylene glycol mono n-butyl ether acetate,or combination thereof. In still other examples, the solvent may be awater-soluble polyhydric alcohol, such as 2-methyl-1,3-propanediol, orcombinations thereof. In still other examples, the solvent may be acombination of any of the examples above. In still other examples, thesolvent is selected from the group consisting of 2-pyrrolidinone,1-(2-hydroxyethyl)-2-pyrrolidone, tripropylene glycol mono methyl ether,dipropylene glycol mono methyl ether, dipropylene glycol mono propylether, tripropylene glycol mono n-butyl ether, propylene glycol phenylether, dipropylene glycol methyl ether acetate, diethylene glycol monobutyl ether, diethylene glycol mono hexyl ether, ethylene glycol phenylether, diethylene glycol mono n-butyl ether acetate, ethylene glycolmono n-butyl ether acetate, 2-methyl-1,3-propanediol, or combinationsthereof.

The solvent may be present in the liquid vehicles in an amount rangingfrom about 0.1 wt % to about 50 wt % (based upon the total weight of thebinder fluid, first fluid, or second fluid). In some examples, greateror lesser amounts of the solvent may be used depending, in part, uponthe jetting architecture of the applicator 24.

As used herein, “liquid vehicle” may refer to the liquid fluid in whichthe polymer particles and/or the metal or metal precursor particles aredispersed. A wide variety of liquid vehicles, including aqueous andnon-aqueous vehicles, may be used. In some instances, the liquid vehicleconsists of a primary solvent with no other components. In otherexamples, the liquid vehicle may include other components, depending, inpart, upon the applicator 24 that is to be used to dispense the binderfluid or first and second fluids.

The primary solvent may be water or a non-aqueous solvent (e.g.,ethanol, acetone, n-methyl pyrrolidone, aliphatic hydrocarbons, orcombinations thereof). In some examples, the liquid vehicles consist ofthe polymer particles and/or the metal or metal precursor particles andthe primary solvent (with on other components). In these examples, theprimary solvent makes up the balance of the liquid vehicle.

Classes of organic co-solvents that may be used in the water-basedliquid vehicles include aliphatic alcohols, aromatic alcohols, diols,glycol ethers, polyglycol ethers, 2-pyrrolidones, caprolactams,formamides, acetamides, glycols, long chain alcohols, or combinationsthereof. Examples of these co-solvents include primary aliphaticalcohols, secondary aliphatic alcohols, 1,2-alcohols, 1,3-alcohols,1,5-alcohols, ethylene glycol alkyl ethers, propylene glycol alkylethers, higher homologs (C₆-C₁₂) of polyethylene glycol alkyl ethers,N-alkyl caprolactams, unsubstituted caprolactams, both substituted andunsubstituted formamides, both substituted and unsubstituted acetamides,or combinations thereof.

Examples of some suitable co-solvents include water-soluble high-boilingpoint solvents (i.e., humectants), which have a boiling point of atleast 120° C., or higher. Some examples of high-boiling point solventsinclude 2-pyrrolidone (boiling point of about 245° C.),2-methyl-1,3-propanediol (boiling point of about 212° C.), andcombinations thereof. The co-solvent(s) may be present in the liquidvehicles in a total amount ranging from about 1 wt % to about 50 wt %based upon the total weight of the binder fluid, first fluid, or secondfluid, depending upon the jetting architecture of the applicator 24.

In some examples, water is present in the binding fluid 36, first fluid,or second fluid, in an amount of at least about 30 wt %, or at leastabout 35 wt %, or at least about 40 wt %, or at least about 45 wt %, orat least about 50 wt %, or at least about 55 wt %, or at least about 60wt %, or at least about 65 wt %, or at least about 70 wt %, or at leastabout 75 wt %, or at least about 80 wt %, or at least about 85 wt %, orat least about 90 wt % based on the total weight of the binding fluid36, or the first fluid, or the second fluid.

Additives

Examples of other suitable binder fluid or first and second fluidcomponents include co-solvent(s), surfactant(s), antimicrobial agent(s),anti-kogation agent(s), viscosity modifier(s), pH adjuster(s) and/orsequestering agent(s). The presence of a co-solvent and/or a surfactantin the binder fluid or first and second fluid may assist in obtaining aparticular wetting behavior with the metal powder build material 16.

Surfactant(s) may be used to improve the wetting properties and thejettability of the binder fluid or first and second fluid. Examples ofsuitable surfactants include a self-emulsifiable, nonionic wetting agentbased on acetylenic diol chemistry (e.g., SURFYNOL® SEF from AirProducts and Chemicals, Inc.), a nonionic fluorosurfactant (e.g.,CAPSTONE® fluorosurfactants from DuPont, previously known as ZONYL FSO),and combinations thereof. In other examples, the surfactant is anethoxylated low-foam wetting agent (e.g., SURFYNOL® 440 or SURFYNOL®CT-111 from Air Products and Chemical Inc.) or an ethoxylated wettingagent and molecular defoamer (e.g., SURFYNOL® 420 from Air Products andChemical Inc.). Still other suitable surfactants include non-ionicwetting agents and molecular defoamers (e.g., SURFYNOL® 104E from AirProducts and Chemical Inc.) or water-soluble, non-ionic surfactants(e.g., TERGITOL™ TMN-6 or TERGITOL™ 15-S-7 from The Dow ChemicalCompany). In some examples, it may be desirable to utilize a surfactanthaving a hydrophilic-lipophilic balance (HLB) less than 10.

Whether a single surfactant is used or a combination of surfactants isused, the total amount of surfactant(s) in the binder fluid or first andsecond fluid may range from about 0.01 wt % to about 10 wt % based onthe total weight of the binder fluid or first or second fluid. Inanother example, the total amount of surfactant(s) in the binder fluid36 may range from about 0.5 wt % to about 2.5 wt % based on the totalweight of the binder fluid or first or second fluids.

The liquid vehicles may also include antimicrobial agent(s). Suitableantimicrobial agents include biocides and fungicides. Exampleantimicrobial agents may include the NUOSEPT™ (Troy Corp.), UCARCIDE™(Dow Chemical Co.), ACTICIDE® M20 (Thor), and combinations thereof.Examples of suitable biocides include an aqueous solution of1,2-benzisothiazolin-3-one (e.g., PROXEL® GXL from Arch Chemicals,Inc.), quaternary ammonium compounds (e.g., BARDAC® 2250 and 2280,BARQUAT® 50-65B, and CARBOQUAT® 250-T, all from Lonza Ltd. Corp.), andan aqueous solution of methylisothiazolone (e.g., KORDEK® MLX from DowChemical Co.). The biocide or antimicrobial may be added in any amountranging from about 0.05 wt % to about 0.5 wt % (as indicated byregulatory usage levels) with respect to the total weight of the binderfluid or first or second fluids.

An anti-kogation agent may be included in the binder fluid or first andsecond fluids. Kogation refers to the deposit of dried ink (e.g., binderfluid or first and second fluids) on a heating element of a thermalinkjet printhead. Anti-kogation agent(s) is/are included to assist inpreventing the buildup of kogation. Examples of suitable anti-kogationagents include oleth-3-phosphate (e.g., commercially available asCRODAFOS™ O3A or CRODAFOS™ N-3 acid from Croda), or a combination ofoleth-3-phosphate and a low molecular weight (e.g., <5,000) polyacrylicacid polymer (e.g., commercially available as CARBOSPERSE™ K-7028Polyacrylate from Lubrizol). Whether a single anti-kogation agent isused or a combination of anti-kogation agents is used, the total amountof anti-kogation agent(s) in the binder fluid or first and second fluidsmay range from greater than 0.20 wt % to about 0.62 wt % based on thetotal weight of the binder fluid or first and second fluids. In anexample, the oleth-3-phosphate is included in an amount ranging fromabout 0.20 wt % to about 0.60 wt %, and the low molecular weightpolyacrylic acid polymer is included in an amount ranging from about0.005 wt % to about 0.03 wt %.

Sequestering agents, such as EDTA (ethylene diamine tetra acetic acid),may be included to eliminate the deleterious effects of heavy metalimpurities, and buffer solutions may be used to control the pH of thebinder fluid 36. From 0.01 wt % to 2 wt % of each of these components,for example, can be used. Viscosity modifiers and buffers may also bepresent, as well as other additives known to those skilled in the art tomodify properties of the binder fluid 36 as desired. Such additives canbe present in amounts ranging from about 0.01 wt % to about 20 wt %.

Unless otherwise stated, any feature described hereinabove can becombined with any example or any other feature described herein.

In describing and claiming the examples disclosed herein, the singularforms “a,” “an,” and “the” include plural referents unless the contextclearly dictates otherwise.

It is to be understood that concentrations, amounts, and other numericaldata may be expressed or presented herein in range formats. It is to beunderstood that such range formats are used merely for convenience andbrevity and thus should be interpreted flexibly to include not just thenumerical values explicitly recited as the end points of the range, butalso to include all the individual numerical values or sub-rangesencompassed within that range as if each numerical value and sub-rangeis explicitly recited. As an illustration, a numerical range of “about 1wt % to about 5 wt %” should be interpreted to include not just theexplicitly recited values of about 1 wt % to about 5 wt %, but alsoinclude individual values and subranges within the indicated range.Thus, included in this numerical range are individual values such as 2,3.5, and 4 and sub-ranges such as from 1-3, from 2-4, and from 3-5, soforth. This same applies to ranges reciting a single numerical value.

Reference throughout the specification to “one example,” “someexamples,” “another example,” “an example,” and so forth, means that aparticular element (e.g., feature, structure, and/or characteristic)described in connection with the example is included in at least oneexample described herein, and may or may not be present in otherexamples. In addition, it is to be understood that the describedelements for any example may be combined in any suitable manner in thevarious examples unless the context clearly dictates otherwise.

Unless otherwise stated, references herein to “wt %” of a component areto the weight of that component as a percentage of the whole compositioncomprising that component. For example, references herein to “wt %” of,for example, a solid material such as polyurethane(s) or colorant(s)dispersed in a liquid composition are to the weight percentage of thosesolids in the composition, and not to the amount of that solid as apercentage of the total non-volatile solids of the composition.

If a standard test is mentioned herein, unless otherwise stated, theversion of the test to be referred to is the most recent at the time offiling this patent application.

All amounts disclosed herein and in the examples below are in wt %unless indicated otherwise.

To further illustrate the present disclosure, examples are given herein.It is to be understood that these examples are presented forillustrative reasons and are not to be construed as limiting the scopeof the present disclosure.

EXAMPLES

Stainless steel build material particles with diameters between 10 μmand 60 μm were layered with a first fluid including copper oxidenanoparticles (having an average particle diameter of 100 nm) and asecond fluid including latex polymer particles. The first fluid andsecond fluid formulations are shown below in Table 1 and Table 2,respectively. Binders were deposited separately (one at a time), buttheir deposition rates were the same (single pen pass deposited the sameamount of each binder).

In all cases, whether when a single binder fluid or two separate fluidswere used, the total deposited binder volume was about 50 g/m² perpowder layer thickness of about 100 μm.

TABLE 1 First Fluid Components wt % 2-methyl-1,3-propanediol 18.02-pyrollidinone 34.0 Tergitol ® 15-S-7 0.9 Tergitol ® TMN-6 0.9Capstone ® FS-35 0.5 Metalon ™ ICI-002HV 15.0 Inkjettable Copper InkActicide ® B20 0.15 Water balance

TABLE 2 Second Fluid Components wt % 2-methyl-1,3-propanediol 9.02-pyrollidinone 16.0 Tergitol ® 15-S-7 0.9 Capstone ® FS-35 0.5 Acryliclatex 16.0 Acticide ® B20 0.15 Water balance

In order to simplify the experiment, the heating in these examples wasdone with rapid heating xenon (Xe) discharge lamp system capable ofraising powder temperature up to point where metal particles can sinterand melt. Material temperature was increased by precisely controlling,energy and time of the Xe lamp discharge. Estimated error of thetemperature “dialing” in this experiment is about 20° C.-30° C. up toabout 500° C.

It is to be understood that other heaters discussed above can be usedinstead of the Xe lamp.

Example 1

FIGS. 4(a)-(d) show the evolution of the second fluid deposited onstainless steel powder and then pulse heating the layers. FIG. 4(a)shows stainless steel powder with the second fluid (including latexpolymer) as-deposited; FIG. 4(b) shows the film-forming state of thelatex polymer on the stainless steel powder after heating at 5.2 J/cm²(about 190° C.); FIG. 4(c) shows the adhesive state of the latex polymeron the stainless steel powder after further heating at 7.9 J/cm² (about250° C.); and FIG. 4(d) shows stainless steel powder with some remainingpyrolyzed latex polymer after further heating at 11.2 J/cm² (about 300°C.). 30 ms pulse was used.

FIGS. 4(a)-(d) show stainless steel metal powder particles onto whichthe second fluid was printed. Heating of the particles caused at firstslow and then rapid disappearance of binder when heated with Xe pulseenergy of around 11 J/cm² corresponding to temperature of about 300°C.-350° C. which triggers pyrolysis of the latex polymer particles. Inthis case, due to the thickness of the stainless steel powder layers andsecond fluid layers, the latex polymer was removed once pyrolysis wastriggered.

Example 2

FIGS. 5(a)-(f) show the evolution of the first fluid and the secondfluid deposited sequentially. The test sample shown in FIGS. 5(a)-(f)was created by depositing the first and second fluids on stainless steelpowder in the following order: layer of the first fluid followed by thesecond fluid, repeated 3 times. FIG. 5(a) shows stainless steel powderand first and second fluids, as-deposited; FIG. 5(b) shows the layersafter heating at 11.3 J/cm² (about 300° C.); FIG. 5(c) shows the layersafter further heating at 15.2 J/cm² (about 440° C.); FIG. 5(d) shows thelayers after further heating at 19.7 J/cm² (about 650° C.); FIG. 5(e)shows the layers after further heating at 24.8 J/cm² (about 800° C.). 30ms pulse was used. FIG. 5(f) shows details of the bonding form in thelayers at the highest pulse energy (about 800° C.). Metal connections(from melted copper nanoparticles) connecting the stainless steel powderparticles can be seen in FIG. 5(f).

Example 3

FIG. 6(a) shows (the second fluid+the first fluid) repeated 3 times.FIG. 6(b) shows (the first fluid+the second fluid) repeated 3 times.FIG. 6(c) shows the first fluid repeated 3 times followed by the secondfluid repeated 2 times.

FIGS. 6(a)-(c) compares fusing of the stainless steel powder particlesat temperature above the pyrolysis temperature (below about 300° C.) forthe latex polymer. Deposition of the second fluid first appears to formlarge sheets of copper connecting particles. While in the case of thefirst fluid being deposited first these sheets are smaller, morefrequently broken and likely providing better binding. Without wishingto be bound by theory, the likely reason for the difference between FIG.6(a) and FIG. 6(b) is related to the removal of latex polymer particlesvia pyrolysis. Differences can be seen in FIG. 6(c) when layers ofcopper oxide (first fluid) are deposited first followed by layers of thelatex polymer particles (second fluid). Latex polymer particles canpyrolyze when on the top layers (FIG. 6(c)) while the underlying copperoxide layers are reduced to elemental copper forming well definedbridges or metal connections connecting adjacent stainless steelparticles.

FIG. 7 is a 2500× magnification of FIG. 6(c) showing stainless steelpowder particles bound together when several layers of the first fluidare deposited first on the stainless steel powder. Copper forms “necks”or metal connections connecting adjacent stainless steel powderparticles. In this case powder was heated to about 450° C.

While several examples have been described in detail, it is to beunderstood that the disclosed examples may be modified. Therefore, theforegoing description is to be considered non-limiting.

What is claimed is:
 1. A multi-fluid kit for three-dimensional printingcomprising: a first fluid comprising a first liquid vehicle comprisingmetal or metal precursor particles; and a second fluid comprising asecond liquid vehicle comprising latex polymer particles dispersedtherein, wherein the latex polymer particles have an average particlesize of from about 10 nm to about 300 nm, and wherein the metal or metalprecursor particles comprise metal nanoparticles, metal oxidenanoparticles, metal oxide nanoparticles and a reducing agent, orcombinations thereof.
 2. The multi-fluid kit of claim 1, wherein thelatex polymer particles are made from (A) a co-polymerizable surfactantchosen from polyoxyethylene alkylphenyl ether ammonium sulfate, sodiumpolyoxyethylene alkylether sulfuric ester, polyoxyethylene styrenatedphenyl ether ammonium sulfate, or mixtures thereof, and (B) styrene,p-methyl styrene, α-methyl styrene, methacrylic acid, acrylic acid,acrylamide, methacrylamide, 2-hydroxyethyl acrylate, 2-hydroxyethylmethacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate,methyl methacrylate, hexyl acrylate, hexyl methacrylate, butyl acrylate,butyl methacrylate, ethyl acrylate, ethyl methacrylate, 2-ethylhexylacrylate, 2-ethylhexyl methacrylate, propyl acrylate, propylmethacrylate, octadecyl acrylate, octadecyl methacrylate, stearylmethacrylate, isobornyl acrylate, tetrahydrofurfuryl acrylate,2-phenoxyethyl methacrylate, benzyl methacrylate, benzyl acrylate,ethoxylated nonyl phenol methacrylate, ethoxylated behenyl methacrylate,polypropyleneglycol monoacrylate, isobornyl methacrylate, cyclohexylmethacrylate, cyclohexyl acrylate, t-butyl methacrylate, n-octylmethacrylate, lauryl methacrylate, tridecyl methacrylate, alkoxylatedtetrahydrofurfuryl acrylate, isodecyl acrylate, isobornyl methacrylate,isobornyl acrylate, acetoacetoxyethyl methacrylate, or combinationsthereof.
 3. The multi-fluid kit of claim 1, wherein the latex polymerparticles comprise 2-phenoxyethyl methacrylate, cyclohexyl methacrylate,cyclohexyl acrylate, methacrylic acid, or combinations thereof.
 4. Themulti-fluid kit of claim 1, wherein the latex polymer particles comprisestyrene, methyl methacrylate, butyl acrylate, methacrylic acid, orcombinations thereof.
 5. The multi-fluid kit of claim 1, wherein thelatex polymer particles are present in the second fluid in an amountranging from about 5 wt % to about 40 wt % based on the total weight ofthe second fluid.
 6. The multi-fluid kit of claim 1, wherein the firstliquid vehicle and the second liquid vehicle comprise water each in anamount of from about 45 wt % to about 75 wt % based on the total weightof the first liquid vehicle and the second liquid vehicle, respectively.7. The multi-fluid kit of claim 1, wherein the metal nanoparticlescomprise, nickel, silver, gold, copper, platinum, or combinationsthereof.
 8. The multi-fluid kit of claim 1, wherein the metal oxidenanoparticles comprise oxides of iron, nickel, silver, gold, copper,platinum, cobalt, manganese, vanadium, molybdenum, or combinationsthereof.
 9. The multi-fluid kit of claim 1, wherein the reducing agentis selected from the group consisting of aldehydes, hydrazides,hydrazine, ascorbic acid, reducing saccharides, or combinations thereof.10. A method of printing a three-dimensional object comprising: (i)depositing a metal powder build material in a powder bed; (ii) based ona three-dimensional object model, selectively applying a first fluid anda second fluid on the metal powder build material in the powder bed,wherein the first fluid comprises a first liquid vehicle comprisingmetal or metal precursor particles, wherein the metal or metal precursorparticles comprise metal nanoparticles, metal oxide nanoparticles, metaloxide nanoparticles and a first reducing agent, metal salts, metal saltswith a second reducing agent, or combinations thereof, and the secondfluid comprises a second liquid vehicle comprising latex polymerparticles dispersed therein, wherein the latex polymer particles have anaverage particle size of from about 10 nm to about 300 nm; (iii)repeating (i), and (ii) at least once to form the three-dimensionalobject; and (iv) heating the powder bed to a temperature of up to about200° C.
 11. The method of claim 10 further comprising: (v) removing thethree-dimensional object from the powder bed and heating thethree-dimensional object to a temperature of up to about 500° C.
 12. Themethod of claim 11, wherein the heating to the temperature of up toabout 500° C. comprises removing at least about 95 wt % of the latexpolymer particles by thermally decomposing the latex polymer particlesand initiate binding of metal powder particles with the metal or metalprecursor particles
 13. The method of claim 10, wherein the latexpolymer particles are present in the second fluid in an amount rangingfrom about 1 wt % to about 50 wt % based on the total weight of thesecond fluid.
 14. The method of claim 11 further comprising: (vi)heating the three-dimensional object in a sintering oven to a sinteringtemperature of greater than about 500° C.
 15. The method of claim 14,wherein the heating of the three-dimensional object in the sinteringoven is to a sintering temperature of greater than about 800° C.